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LONDON (Reuters) - Global warming could trigger hurricanes, or tropical cyclones, over the Mediterranean sea, threatening one of the world's most densely populated coastal regions, according to European scientists.

Hurricanes currently form out in the tropical Atlantic and rarely reach Europe, but a new study shows a 3 degrees Celsius (5.4 degrees Fahrenheit) rise in average temperatures could set them off in the enclosed Mediterranean in future.

"This is the first study to detect this possibility," lead researcher Miguel Angel Gaertner of the University of Castilla-La Mancha in Toledo, Spain, told Reuters on Monday.

"Most models in our study show increasing storm intensity and if you combine this with rising sea levels, as are projected, this could be damaging for many coastal settlements."

As well as being home to millions, the Mediterranean coast is also a major centre of tourism, which would be under threat.

Factors influencing hurricanes include warm sea surface temperatures and atmospheric instability. In the past, they have been confined to a limited number of regions, such as the north Atlantic and north Pacific, where they are known as typhoons.

Recently, however, they have been forming in unusual places, which Gaertner sees as a clear danger signal.

In 2004, Hurricane Catarina formed in the south Atlantic and hit land in southern Brazil. A year later, Hurricane Vince formed next to the Madeira Islands and became the first to make landfall in Spain.

In a paper published in the American Geophysical Union Journal, Gaertner and colleagues from the Max Planck Institute for Meteorology in Hamburg, Germany, used a range of regional climate models to assess the chance of similar events in the Mediterranean.

They found rising temperatures pointed to increasing storm intensity and, in the case of the most sensitive computer model, a likelihood of strong hurricanes.

Gaertner said a large number of uncertainties remained and it was not yet possible to say which parts of the Mediterranean would be hardest hit. He also believes there is time to avoid the worst-case scenario by working to limit global warming.

"This is a big threat but I think we have time to avoid it, if we cut emissions of greenhouse gases," Gaertner said.

A United Nations climate panel, drawing on the work of 2,500 scientists, said this year that the "best estimate" was that temperatures would rise 1.8-4.0 Celsius this century.

Most experts say emissions of greenhouse gases, mainly from burning fossil fuels in power plants, factories and cars, are the principal reason for rising temperatures.